Space shuttle Discovery lifts off from launch pad 39A at the Kennedy Space Center on February 24, 2011 in Cape Canaveral, Florida. As the Shuttle Program winds down, Space Shuttle Discovery is on its 39th and final mission to the International Space Station. (Photo by Joe Raedle/Getty Images). CAPE CANAVERAL, FL – FEBRUARY 24

In this handout photo provided by NASA, Space Shuttle Discovery kicks off the Fourth of July fireworks with its own fiery display as it launches, spewing foam and smoke over the ground, on mission STS-121 July 4, 2006 at the Kennedy Space Center in Cape Canaveral, Florida. It was the third launch attempt in four days; the others were scrubbed due to weather concerns. Liftoff was on-time at 2:38 p.m. EDT. During the 12-day mission, the STS-121 crew of seven will test new equipment and procedures to improve shuttle safety, as well as deliver supplies and make repairs to the International Space Station. Landing is scheduled for July 17 at Kennedy's Shuttle Landing Facility. (Photo by Regina Mitchell-Ryall, Tony Gray/NASA via Getty Images). CAPE CANAVERAL, FL – JULY 4 2006

Space shuttle Discovery lifts off from launch pad 39A at the Kennedy Space Center on February 24, 2011 in Cape Canaveral, Florida. As the Shuttle Program winds down, Space Shuttle Discovery is on its 39th and final mission to the International Space Station. (Photo by Joe Raedle/Getty Images). CAPE CANAVERAL, FL – FEBRUARY 24

The moon is seen near the Space Shuttle Discovery STS-119 as it sits on the launch pad while it is prepared for launch March 11, 2009 in Cape Canaveral, Florida. The Discovery is being prepared for the scheduled launch date of March 11, 2009 on a mission to the international space station. (Photo by Eliot J. Schechter/Getty Images). CAPE CANAVERAL, FL – MARCH 11 2011

In this handout provided by NASA, Backdropped by a blue and white Earth, Space Shuttle Discovery approaches the International Space Station during STS-120 rendezvous and docking operations October 25, 2007. Docking occurred at 7:40 a.m. (CDT) on Oct. 25, 2007. The Harmony node is visible in Discovery's cargo bay. (Photo by NASA via Getty Images). IN SPACE – OCTOBER 25 2007

A NASA worker walks near the Space Shuttle Discovery as it is towed to the Orbiter Processing Facility after landing at Kennedy Space Center November 7, 2007 in Cape Canaveral, Florida. Discovery successfully completed its15-day build and repair mission to the International Space Station. (Photo by Eliot J. Schechter/Getty Images). CAPE CANAVERAL, FL – NOVEMBER 7 2007

Space Shuttle Discovery lands in the Mojave Desert on September 11, 2009 at the NASA Dryden Flight Research Center on Edwards Air Force Base near Mojave, California. The STS-128 was prevented from landing at the preferred site at the Kennedy Space Center by deteriorating weather on the east coast of Florida. (Photo by David McNew/Getty Images). EDWARDS, CA – SEPTEMBER 11 2009

The Space Shuttle Discovery lifts off from launch pad 39-A at Kennedy Space Center on May 31, 2008 in Cape Canaveral, Florida. Discovery is en route to the International Space Station on a construction mission. (Photo by Eliot J. Schechter /Getty Images). CAPE CANAVERAL, FL – MAY 31 2008

In this handout image provided by NASA, backdropped by a blue and white part of Earth, the aft section of space shuttle Discovery, currently docked with the International Space Station February 26, 2011 in Space. Discovery, on its 39th and final flight, is carrying the Italian-built Permanent Multipurpose Module (PMM), Express Logistics Carrier 4 (ELC4) and Robonaut 2, the first humanoid robot in space to the International Space Station. (Photo by NASA via Getty Images). IN SPACE – FEBRUARY 26 2011